The present invention relates to charged particle beam apparatuses and pattern measuring methods and more particularly, to a charged particle beam apparatus for aligning charged particles given off from a sample to detect them and a pattern measuring method therefor.
As a semiconductor pattern becomes corpuscular, a delicate difference in configuration has an influence upon operational characteristics in a device and accordingly, needs for management of configuration have been raised. Therefore, a scanning electron microscope (SEM) used for inspection and measurement of semiconductors has been required of high sensitivity and high accuracy than in the past more and more. Especially, highly efficient detection of signals given off from a bottom or the like of such a pattern of large aspect ratio (depth/width) as a deep hole or trench has been demanded.
In this case, how to detect efficiently a signal among discharged signals of less amounts is important and thus, making full use of discrimination of angle and direction of detection signals can be one of solving measures. JP-A-09-507331 discloses a SEM having two-stages of detectors adapted to discriminatively detect, for the sake of forming a high contrast mage of a hole bottom on the basis of electrons discharged from the bottom of such a deep hole as a contact hole, electrons passing through a trajectory close to the optical axis of an electron beam by having a small relative angle to the optical axis, that is, high angle electrons and electrons passing through a trajectory relatively distant from the optical axis of the electron beam by having a larger relative angle to the optical axis in contrast to the high angle electrons, that is, low angle electrons. Further, disclosed in JP-A-2006-228999 and JP-A-2006-332038 is a SEM having an aligner for secondary electrons adapted to control trajectories of secondary electrons with the aim of unifying signals detected by means of a plurality of detectors.
By selectively detecting electrons in the specified directions on the basis of angle discrimination as explained in the JP-A-09-507331, JP-A-2006-228999 and JP-A-2006-332038, an image emphasizing information indicative of the hole bottom or the like can be formed. Of the electrons discharged from the hole bottom, however, electrons discharged from a portion near the side wall have a high possibility of impinging upon the side wall and the efficiency of detection of them is lowered. Especially when outputs of the right and left detectors are attempted to be uniform as explained in JP-A-2006-228999 and JP-A-2006-332038, values of brightness at the left and right edges are unified in the case of an objective of a hole pattern and there is a possibility that a signal of one edge cannot be detected sufficiently. In particular, with a critical dimension-scanning electron microscope (CD-SEM) used, highly accurate measurement is difficult to realize unless both the two edges representing measurement references have each a high S/N ratio.